Phasing Phased-Out???

Discussion in 'Amps and Cabs [BG]' started by rickbass, Apr 16, 2001.

  1. rickbass

    rickbass Supporting Member

    Past threads and posts have mentioned using multiple cabs that weren't originally married together.

    In the 80's and early 90's, it seemed as though the subject of speaker phasing for multiple cabs was always a topic. A couple of bands I was with years ago had a tech, (they used to be "roadies"), who made sure our speakers were in phase.
    I don't see the topic discussed anymore and I get around a lot.

    Is this still an important consideration, or did some technological breakthrough occur is the mid-late `90's that made this a non-issue?
  2. MikeyD


    Sep 9, 2000
    Hi, Rick! Phase it - I still think it's an issue. ;) But maybe most manufacturers have agreed among themselves about driver phasing vs. input, so that might help. In fact recently (pertinent to our Carvin-equipped friends) I wondered if some of the problems dudes have had with Carvin heads not working right is they may have plugged two speakers into each channel of the Redline amp and had the bridge switch on. I haven't tried it, but according to the wiring diagram I have, this will feed the respective speakers signals that are 180 degrees out of phase. Since a lot of the bass energy would be canceled in air by this phasing, the amp would tend to sound very lame and the user might crank it up to "11" to compensate. This might eventually cause thermal shut-off, etc. Just a thought.

    Recently I started stacking my RC210 atop my new Eden 2x15 cabinet. The corners aren't quite compatible, so it was easier to set the RC210 back about 4", but then I got thinking about funny phasing at higher frequencies (say 800-1000 Hz. and above), so I fixed it so I could make sure the grilles were flush.

    Beyond this, I don't know. It's still something to be aware of - especially if it's an older speaker or if the wiring has been changed since manufacture.

    Phasing of woofers is easy to check, though, if you can see the cones. Just hook up a battery to the terminal and note which way the cones move. All the speakers in the stack should show the same motion when the battery is connected the same way.
    - Mike
  3. Hey guys! Phase is very important. Well for bass rigs, correct polarity and physically aligning the speakers is probably sufficient. For PA it's critical. Many of the dedicated system controllers and generic digital speaker processors have very complex phase correction and time alignment algorithms. These take into account physical and electrical sources of phase problems. Proper phase and time alignment makes a huge difference in the sound quality of a PA. A 1ms delay between two speakers can cause broadband comb filtering and huge anomolies in sound. 1ms! that's a pretty small delay. The phase correction of PA systems is getting fairly advanced, too. A lot of the new flying hardware makes it possible to be very precise in the aiming of speakers. That coupled with the sophistcated processing and measurment systems, is making hifi sound in arenas a possibility. Meyer Sound's Self Powered system claims a phase response of +/- 35 degrees from 26Hz to 19kHz. That's better than most hifi systems. This rig sounds incredible, when flown right and calibrated properly. I did a string of shows in Canada with Chris de Burgh as systems engineer with this PA, and couldn't believe how hifi it sounded in cavernous hockey arenas (Molson Center, Air Canada Center etc). This is almost entirely due to proper phase alignment....oops, I wrote a (boring) novel again. Sorry, I just love this stuff and I can yak about it forever :D Gotta go study LaPlace transforms......
  4. Excellent post man! I love that S domain. Laplace kicks Fourier's butt! :D

  5. Haven't gotten to Fourier yet, but I hear they're lots of fun. My first signals course is next year so I'll have Fourier out the wazoo then! :D I can't wait for this term to be over (finished Saturday), it's been rough. I got a 4 month work term being a soundguy again (or being a fulltime soundguy):D woohoo. And I'll have time to do that cap job on the old SVT too!
  6. MikeyD


    Sep 9, 2000
    LOL!! I wouldn't go that far...! Anyway, Space makes a good point about phase response in systems that handle the full spectrum. It makes a lot of sense, although I still think that reflections/echoes from a really live (echoey) space can throw a wrench in the works, even with a fully phase-coherent system.

    Space - good luck on your transforms! When/if you study electromagnetic wave propagation, I suspect you'll get into analogous stuff regarding diffraction, interference, phasing, etc. The math can get super ugly, though! And it's still not quite the same as acoustics in air.

    - Mike (fellow wave nerd)
  7. rickbass

    rickbass Supporting Member

    Man! I hoped for responses from guys as qualified as you all. THANKS!!!

    It's just that it seems like I see all these posts about people hooking up cabs willy-nilly and no one ever seems to mention phasing. I look at catalogs with rigs that use multiple cabs and never see one word about, "and rest assured, these cabinets are in-phase when they arrive at your door."

    I found out the hard way in the `60's when I hooked up a 2 blackface Bassmans, thinking I'd really have some sound. Turns out, they were out of phase and my sound was actually worse :eek:

    Spacegoat - What I'd give to have you at the board....
  8. jcadmus


    Apr 2, 2000
    I'd be lying to you if I said I was following this discussion.

    But I'll add this -- listen to a couple cabs that are OUT of phase, and you'll KNOW it's an issue.

    If it's loud enough, the frequency cancellation and the oscillation will make you think you stuck your head in a blender.
  9. Gabu


    Jan 2, 2001
    Woodland Hills, CA

    I am so curious now if my amp is "in phase" or not. Does it make as much a difference if you biamp as opposed to doing all your speakers full range?
  10. rickbass

    rickbass Supporting Member

    g - It really only becomes an issue when you're hooking up more than one cab, especially for bassists, since out of phase speakers kill bass more than any other frequency range (as I mentioned about the 2 Bassmans).

    While the cones of one cab are moving outwards, the other cab's(s') are moving inwards. You are actually getting LESS sound using more cabs as they work against each other. I don't see bassists mentioning this much, but I do see them talk a lot about hooking up various cabs.

    To check;
    - grab the 9V battery out of your bass/spare, and with the head turned off unplug the speaker cable from the head but leave the cabinet end connected.
    - Touch the + (positive) battery terminal to the tip of the cable jack and the - (negative) terminal to the sleeve of the jack. The cone should move outwards. When you take the battery away, the cone should return to it's resting position
    -Repeat with the other cab/cabs. If the cone/cones move in the opposite direction your sound will suck because the speakers are wired out of phase.

    As for horns, obviously you don't have cones to watch. The only thing I know to do is what a sound guy showed me. He had this thing he rents at a sound/music store called a phase popper system, (Spacegoat may know what this really is), that he hooked to "send" of the board. It makes a popping noise through all the speakers and horns in the system and has a box that is held in front of the cabs and registers different colors for in/out of phase.
  11. First of all, thanks for the compliment Rickbass! The phase popper is pretty much exactly as you described it. It just compares the electrical signal causing the pops to the acoustic signals from the speakers. It basically tell whether the speakers all have the same polarity. Having a speaker with the polarity backwards will cause the acoustic signals to be 180 degrees out of phase from one with correct polarity. This is not a big issue if you have a single speaker because there's no reference point. The 180 degrees out scenario is the most extreme case and is very noticeable in low end. It gets less and less noticeable with increasing frequency. Biamping causes phase anomolies, but so does running, say, a 15 and a 210 fullrange. The different sized speakers and different cabs will have somewhat different phase responses. Especially when they are reproducing the same information This is normal and not a big deal. Crossovers introduce phase shift as a function of their circuit design. The order of the filters used causes the output signals to be phase shifted. A first order filter (ie 6dB/octave rolloff)will introduce 90 degrees of phase shift. Each order added gives 90 degrees of shift. Common crossovers are usually 12 or 18dB/octave. This is just the rolloff slope on either side of the crossover point. So if your crossover is set at say 200 Hz 12dB/octave, the low and high outputs would produce the same output of 200 Hz, say 0dB (unity) for reference. So if you ran a test tone of 400Hz through this setup, the high output would produce that frequency but at 12dB less output than a 200 Hz tone. This phase shift between bandpasses is nothing to be concerned about with a biamped bass rig, but it definately becomes an issue in a PA system. Some systems actually intentionally wire a bandpass out of phase from the other bandpasses to improve phase performance. Certain cabinet designs can introduce phase shifts. Does anyone remember the old modular Martin PAs? The mid cabs look like Philishave razors :D. They suggested running them out of phase from the lows and highs. Here's something I just thought about: If you're going to replace a speaker with a JBL driver, flip the polarity of the JBL opposite to that of your other speakers. (ie red to black) JBLs have the opposite polarity to other speakers, because they wind the coils in the opposite direction! I knew a guy who had a 215 and replaced one of the RCFs with a JBL. When he fired it up it wasn't half as loud as before, because he just wired it up like any other driver, so the two were 180 degrees out. Oh my, another novel. Please tell me to shut up if I'm boring you! :p
  12. jvtwin

    jvtwin What it needs is a little more cowbell

    Jan 26, 2001
    LA Calif.
    Stupid question (like many others I've asked) but wouldn't this only become an issue if you were mix/ matching speakers in a cab or using different brand cabs together? In most every match (brand) cab I've used in the past, this was never a problem.

    Just curious.

    I'll go back to sleep now.
  13. rickbass

    rickbass Supporting Member

    I don't think anyone smart enough to figure out how to corral an Aguilar asks "stupid" gear questions, :D

    I've used matched multiple cabs that were out of phase, Sunn, Fender, Guild come to mind. But I haven't had that embarassment for years, (the Fenders were blackface), and that's why I wondered about the new stuff. Haven't used many multiple cabs in recent years...mainly my Carvin stack.

    But I was toying with the idea of slaving the R600 off the R1000 and adding the Cyclops to it for grins :eek:
  14. jvtwin

    jvtwin What it needs is a little more cowbell

    Jan 26, 2001
    LA Calif.
  15. One old Altec paper said it was actually better to run the horn out of phase with the woofer in a 2-way system. When run in phase, with a 2nd order crossover, there is a hard response dip at the crossover frequency where the two signals mix. But if you run the horn and woofer out of phase, this big dip mixes into a small 3 dB peak. Much nicer than the like -30dB notch!

    I think the best solution in this case is a 3rd order crossover, which when running the horn and woofer out of phase, gives you an excellent almost linear phase plot for the entire spectrum. The goal of HIFI is to have a flat frequency response, as everybody knows, but the other requirement is that the phase response is linear, not necessarily flat, but linear. The slope of the linear phase plot translates into a constant delay in the time domain.


  16. jcadmus


    Apr 2, 2000
    Important tip here -- if you're experiencing this problem, it may not be the cabs. It may be the speaker cables you're using -- especially if they're homemade.

    If the wires are soldiered to the tip and sleeve one way on one plug and the opposite way on the other plug, you can run into this problem.

    That happened to me once.